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Space Station Science

Picture of the Day

April 21, 2003

The Physics of Space Gardens

Credit: ISS Expedition 6 Flight Engineer Nikolai Budarin

Explanation: It could only happen in space: A tiny bubble of air
hangs suspended inside a droplet of water. The droplet rests in the
cup of a delicate green leaf, yet the stalk doesn't bend at all. 

Cosmonaut Nikolai Budarin photographed this scene on April 9, 2003.
He was peering into the Russian Lada greenhouse onboard the
International Space Station (ISS), and his snapshot illustrates some
of the strange physics of gardening in space. 

First, consider what would happen on Earth: The air bubble, lighter
than water, would race upward to burst through the surface of the
droplet. Meanwhile, the leaf would be busy tipping the heavy water
onto the floor below. Everything would be in motion, the picture a
blur. 

In Earth-orbit, though, the scene is truly motionless. The air bubble
doesn't rise because it is no lighter than the water around
it--there's no buoyancy. The droplet doesn't fall from the leaf
because there's no force to pull it off. It's stuck there by
molecular adhesion. 

Sticky water. No buoyancy. These are some of the factors spacefarers
must take into account when they plan their gardens. Suppose Budarin
sprays water onto the base of the plant. Will it trickle down to the
roots? More likely it will stick to the stem or adhere the substrate
in which the plant grows. And what happens to oxygen emitted by
plants? Without buoyancy to stir things up, air circulation can be
poor. Oxygen lingers. It doesn't waft away to make room for the
carbon dioxide plants need. A plant can actually suffocate in its own
emissions! 

Nevertheless, plants can flourish in spaceships. Recent experiments
onboard the ISS prove it. Stay tuned this week and we'll show you
some of the eye-catching results. 

Credits & Contacts
Author: Dr. Tony Phillips 
Responsible NASA official: Ron Koczor 
Production Editor: Dr. Tony Phillips 
Curator: Bryan Walls 
Media Relations: Catherine Watson

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